The new study arrives at a slightly lower annual figure of 19,000, a difference the lead author of the COMEAP study, Fintan Hurley, attributes to differing methodology.

Breaking down pollution

The latest study adds to the debate by breaking down mortality rates according to sector - transport, energy and industry.

The researchers combine models of atmospheric circulation and chemistry with source data and clinical studies to arrive at their independent figures for the health effects of pollution.

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The findings challenge the traditional view that industrial plants are the main source of pollution

Although the popular perception of air pollution involves images of smoke stacks billowing out toxic black fumes into the atmosphere, industry and the power sector turn out to kill fewer than vehicle emissions, the data shows.

"Cars and lorries emit right by where people live and work and so have a greater impact," explains lead author Steven Barrett.

The findings also pinpoint where the deaths happen: 2,200 every year in Greater London, another 630 in both Greater Manchester and West Midlands.

Because the model includes Europe-wide weather patterns, it also reveals how far the deadly effects of air pollution can reach.

Of the 19,000 annual UK deaths estimated, 7,000 are due to pollutants blown in from the continent. In London, European pollutants add 960 deaths each year to the 2,200 caused by UK combustion fumes.

But the international trade in deaths goes both ways. More than 3,000 European deaths can be attributed to UK emissions the authors say.

"We are all in this together," agrees Fintan Hurley of COMEAP.

"If one city were to clean up its traffic, it would still be dealing with pollution from traffic elsewhere."

We estimate the premature deaths are costing the UK at least £6 billion a yearDr Steven Barrett, Study co-author

The propensity for air pollution to straddle boundaries has political, as well as medical, implications.

The UK is currently facing the threat of prosecution by the European Union for serial violations of air-quality standards.

But the new study suggests that 40% of the key pollutant, PM2.5 (particles up to 2.5 micrometres in diameter) comes from abroad.

"The EU-attributable particulates in London are likely to have significantly contributed to the violations, because they raised the background concentration on which local short-term peaks were superimposed," explains Steven Barrett.

Not that these legal niceties are of any help to those most at danger from polluted air. The analysis identifies key improvements that would help reduce the health burden of air pollution.

Practical measures include the reduction of black carbon emitted in car exhausts - especially from older cars that fail to burn their fuel completely.

Reductions in nitrogen oxide (NOx) emissions would also help, though perhaps at a cost of making vehicles less efficient.

Far more effective, experts say, would be to invest in public transport, taking cars off the road altogether.

Such improvements would come at a cost, but so does continuing with business as usual.

"We estimate the premature deaths are costing the UK at least £6 billion a year," says Steven Barrett, "and perhaps as much as £60 billion."

For comparison, Crossrail is projected to cost £14.8 billion to build and expected to remove 15,000 car journeys during the morning peak.

Meanwhile, Steven Barrett is moving his attention to another form of public transport, and hopes soon to conclude a detailed assessment of the health impacts of either a third runway at Heathrow and of the alternative Thames Estuary Airport proposal.